Magnetic recording media has begun to incorporate perpendicular magnetic recording (PMR) technology in an effort to increase areal density and is now working toward densities of 800 Gbits/in2. Generally, PMR media may be partitioned into two primary functional regions: a soft magnetic underlayer (SUL) and a magnetic recording layer(s) (RL). FIG. 1 illustrates portions of a conventional perpendicular magnetic recording disk drive system having a recording head 101 including a trailing write pole 102 and a leading return (opposing) pole 103 magnetically coupled to the write pole 102. An electrically conductive magnetizing coil 104 surrounds the yoke of the write pole 102. The bottom of the opposing pole 103 has a surface area greatly exceeding the surface area of the tip of the write pole 102. As the magnetic recording disk 105 is rotated past the recording head 101, current is passed through the coil 104 to create magnetic flux within the write pole 102. The magnetic flux passes from the write pole 102, through the disk 105, and across to the opposing pole 103 to record in the PMR layer 150. The SUL 110 enables the magnetic flux from the trailing write pole 102 to return to the leading opposing pole 103 with low impedance.
Higher areal densities are typically achieved with well-isolated smaller grains in the PMR layer 150. A higher magnetic anisotropy constant (Ku) is typically required to resist the demagnetization effects of the perpendicular geometry and to keep the smaller grains thermally stable to reduce media noise. US patent publication 2004/0185307 describes magnetic recording layers employing an ordered alloy such as CoPt and FePt having an L10 structure. While such an L10 ordered alloy can exhibit a high Ku that is beneficial for thermal stability and reduction of noise, due to the limit of a head writing field, media with such high magnetic anisotropy may exceed a coercivity threshold and may not be recordable by the recording head 101.
The writing field of high anisotropy media can be decreased using an exchange coupled composite (ECC) media in which a composite recording layer employs a magnetic soft layer to exchange couple a magnetic hard layer. For such ECC media, the magnetically soft region will switch in presence of an external field (e.g., applied by recording head 101) and apply a magnetic torque assisting a switching of the magnetically hard region and thereby decreasing the media writing field required for highly anisotropic media. A non-FePt ECC media with hard and soft magnetic layers separated by a nonmagnetic exchange coupling layer has been demonstrated by J. P. Wang et al., Exchange Coupled Composite Media for Perpendicular Magnetic Recording, IEEE Trans. on Magnetics, Vol. 41, No. 10, 3181 (October 2005). However, for L10 FePt high anisotropy media, the concept of exchange coupling assisted composite media has only been demonstrated without an exchange coupling interlayer. For example, formation of a soft magnetic FePtC layer on a hard magnetic FePtC layer is described in J. S. Chen, et al., High Coercivity L10 FePt Films with Perpendicular Anisotropy Deposited on Glass Substrate at Reduced Temperature, Appl. Phys. Lett., Volume 90, Issue 4 (2007). In Chen, et al., reliance on carbon segregation between the hard and soft magnetic layers results in exchange coupling that is uncontrolled. As such, an EEC construction in L10 FePt-based media is heretofore unknown.